n,m=map(int,input().split())
l=[int(input()) for _ in [0]*m]
x=t=0
for i in [0]*n:
	D=[abs(d-x) for d in l]
	j=min(D)
	k=D.index(j)
	t+=j
	x=l[k]
	l.pop(k)
print(t)